In a conventional computer apparatus, the commonly used power supply method is based on the PWM (Pulse Width Modulation) method to reduce the input voltage, such as 5V or 12V, to the voltage required for each element, such as 1.05˜1.825V or 1.3˜3.5V). The main elements used in PWM circuit comprise a PWM chip, a MOSFET (Metal oxide semiconductor field effect transistor), an inductive coil, and a filter capacitor, etc. However, in the actual operating process of a computer apparatus, because the motherboard is conducting large current continuously, the elements on the motherboard will be easily heated. If these elements don't have very good heat sinks for heat dissipation, they would be burned down. In fact, in the operating process of motherboard in the prior art, MOSFET elements, particularly High-Side-MOS, would be easily burned down due to too high the temperature. At this time, although the motherboard would execute a self-protection function to shutdown, if the computer is rebooted, the voltage of CPU would be raised simultaneously with the voltage supplied by the power supply, i.e. 12V; finally, the CPU would be failed by over-voltage and resulting in too high voltage and burning down. Furthermore, each kind of protection functions for power supply would have larger time delay, and could not protect in time. For the prior art, there was no complete solution provided for the over-voltage protection of CPU, so there should be a lot of improvement possibilities.